The present invention relates to the making of a support for a tire tread band used inside tires for supporting the load in the event of loss of inflation pressure. More precisely, it concerns supports having at their base a substantially non-extensible reinforcement framework produced by means of reinforcement elements of the type which can reinforce tires. It also concerns the methods of manufacturing such supports.
Patent application EP 0 796 747 describes a particular example of such a support, made from flexible material, for example based on saturated-chain elastomers such as EPDM rubber. FIG. 1 of this application and the corresponding passage in the description show and describe that the base of the bearing support is reinforced by elements disposed substantially circumferentially.
Different techniques of manufacturing a molded object are known: compression molding and materials transfer molding, and this category can include injection molding as well as flow molding. Compression molding assumes the introduction of the necessary volume of rubber inside the mould before closing it, whereas injection or flow molding assume the closure of the mould before the introduction of the volume of rubber or products required. Injection molding consists of injecting, into the closed mould, the material forming the final product under given conditions of pressure and temperature; as for flow molding, it differs from injection by the fact that the base products are introduced into the flow mould under precise operating conditions, said basic products reacting together in the mould in order to give the material of the finished product.
The different techniques involving the introduction of material into a closed mould do not lend themselves well to non-homogeneous finished products and in particular products reinforced by flexible reinforcement elements. These techniques are not well adapted when the reinforcements are wire or cable plies separated from each other: the rubber driven into the mould entrains with it the reinforcement elements or at least deforms and/or moves greatly the elements. Hence, it is practically impossible to ensure a precise positioning of said elements in the finished product and consequently to obtain correct, uniform and repeated reinforcement properties. This is one of the prime reasons why the technique of force feeding material into a closed mould, for rubber parts reinforced by wires or cables, has never shown itself to be advantageous and propitious for obtaining high-quality products. It is for example well known that normal tires, in spite of many attempts, are not currently injected or obtained by casting: one makes first a non-vulcanized or raw blank with a form fairly close to the final manufactured form where the blank includes the reinforcement elements inserted at the required places between the different layers of elastomer material. Then the molding is carried out by enclosing the molding elements of the vulcanization mould around the blank.
To resolve the problems of positioning the reinforcement elements during the manufacture of a support by a technique of force feeding material, application EP 1000774 proposes for the elements for reinforcing the base of said support the use of substantially no-extensible circumferential elements used in the form of a calendered ply made of rubber material with complementary reinforcement elements disposed, at least partly, radially outside the circumferential reinforcement elements and axially opposite the feed points disposed at the body of the support. Preferably, the complementary reinforcement elements comprise elements oriented with respect to the circumferential direction at an angle greater than 60° and also being in the form of a calendered ply of rubber material.